The proposed research aims to evaluate the role of calmodulin in mediating the control by Ca2 ion of intracellular enzymes in nerve cells and in human erythrocytes. Calmodulin in erythrocytes stimulates the Ca 2 ion transport ATPase. The erythrocyte protein appears to be identical with calmodulin from bovine brain, and both proteins stimulate the cyclic nucleotide phosphodiesterase from brain. It is proposed to investigate the relationship between calmodulin and the Ca2 ion transporting ATPase in brain and to demonstrate its activation of pumping of Ca2 ion out of the brain cell. Physical studies, studies on binding of calmodulin to ATPase in brain and in human erythrocytes and kinetic studies will be carried out.